1. Field of the Invention
The present invention relates to a fixing device in an image-forming apparatus.
More specifically, the present invention relates to a fixing device comprising:                a fixing part for conveying a sheet of paper that is held between a pressure body and a fixing body that are rotatably supported about substantially parallel shafts while simultaneously fixing supported unfixed toner; and        a separation mechanism for separating the sheet of paper, which is carried away from the fixing part, from the fixing body or pressure body; wherein        the separation mechanism has a separation member provided with a separation pawl for separating the sheet of paper and a shaft member, a support part for pivotably supporting the separation member via the shaft member so that the separation pawl can be brought near to and separated from the fixing body or pressure body, a first urging mechanism for urging the separation member in a direction in which the separation pawl approaches the fixing body or pressure body, and a control part for controlling the pivoting range of the separation pawl toward the fixing body or pressure body by applying a contact pressure;        the shaft member is provided so as to be movable between an initial position on the support part for the separation, and a retracted position that is set apart from the fixing part with respect to the initial position;        the urging force created by the first urging mechanism operates such that a pressing force is generated in a direction in which the shaft member is displaced from the retracted position toward the initial position; and        the magnitude of the pressing force is set such that the shaft member is moved from the initial position to the retracted position by a contact pressing force exerted on the separation pawl by a jammed sheet of paper.        
2. Description of the Related Art
An example of a fixing device according to prior art is disclosed in Japanese Laid-open Patent Application No. 2005-31350. In the fixing device according to the prior art, the magnitude of a pressing force created by a first urging mechanism that presses a shaft member toward an initial position is usually set to a value at which the shaft member is displaced from the initial position to a retracted position by a contact force exerted on a separation pawl by a jammed sheet of paper so that a state is not created in which the contact pressure created by the jammed sheet of paper causes the separation pawl to firmly press against a fixing surface or pressure surface and damage the fixing surface or pressure surface.
However, in the fixing device, even in a normal state in which a sheet of paper is not jammed, when a sheet of paper is firmly adhered against the fixing surface or pressure surface, the separating pawl, which is inserted between the adhering sheet of paper and the fixing surface or pressure surface, may be pressed by the adhered sheet of paper and made to resist the pressing force of the first urging member so that the shaft member will be moved to the retracted position. The separation pawl will be separated from a position preferable for separating the sheet of paper that is in the vicinity of the fixing part, and the sheet of paper will be impossible to be separated.
In order to resolve the foregoing problem, if the pressing force created by the elastic urging force of the first urging mechanism on the shaft member is set to a high value, the separation pawl will be pressed against the fixing surface or pressure surface with excessive force even in a normal state in which a paper jam has not occurred, and a risk arises that the fixing surface or pressure surface will be damaged by the separation pawl.